EUV radiation modification methods and systems

ABSTRACT

A method and system for generating EUV light includes providing a laser beam having a Gaussian distribution. This laser beam can be then modified from a Gaussian distribution to a ring-like distribution. The modified laser beam is provided through an aperture in a collector and interfaces with a moving droplet target, which generates an extreme ultraviolet (EUV) wavelength light. The generated EUV wavelength light is provided to the collector away from the aperture. In some embodiments, a mask element may also be used to modify the laser beam to a shape.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/491,363, filed Apr. 28, 2017, the entire contents of which are herebyincorporated by reference.

BACKGROUND

The electronics industry has experienced an ever increasing demand forsmaller and faster electronic devices which are simultaneously able tosupport a greater number of increasingly complex and sophisticatedfunctions. Accordingly, there is a continuing trend in the semiconductorindustry to manufacture low-cost, high-performance, and low-powerintegrated circuits (ICs). Thus far these goals have been achieved inlarge part by scaling down semiconductor IC dimensions (e.g., minimumfeature size) and thereby improving production efficiency and loweringassociated costs. However, such scaling has also introduced increasedcomplexity to the semiconductor manufacturing process. Thus, therealization of continued advances in semiconductor ICs and devices callsfor similar advances in semiconductor manufacturing processes andtechnology.

As merely one example, semiconductor lithography processes may uselithographic templates (e.g., photomasks or reticles) to opticallytransfer patterns onto a substrate. Such a process may be accomplished,for example, by projection of a radiation source, through an interveningphotomask or reticle, onto the substrate having a photosensitivematerial (e.g., photoresist) coating. The minimum feature size that maybe patterned by way of such a lithography process is limited by thewavelength of the projected radiation source. In view of this, extremeultraviolet (EUV) radiation sources and lithographic processes have beenintroduced.

However, generating the EUV light (or radiation) for EUV system can bean energy intensive and difficult process to control. In some EUVsystems, for example, which utilize a plasma to generate the EUVradiation there can be a substantial energy waste. The wasted EUVradiation not only is costly in efficiency, but also generates a heatthat requires dissipation. Thus, EUV light generation systems have notproved entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic view of an EUV light (also referred to as EUVradiation) source system, including an exemplary EUV vessel, inaccordance with some embodiments;

FIGS. 2A, 2B, 2C, and 2D are exemplary diagrammatic views of an EUVlight source system including a laser beam impacting a particle ordroplet and generation of EUV light therefrom, in accordance with someembodiments;

FIGS. 3A, 3B are an exemplary diagrammatic views of an embodiment of abeam transport and/or focus system of an EUV light source system, inaccordance with some embodiments;

FIG. 4 is an exemplary schematic view of a further embodiment of a beamtransport and/or focus system of an EUV light source system, inaccordance with some embodiments;

FIG. 5 is an exemplary schematic view of a collector of an EUV lightsource system, in accordance with some embodiments;

FIG. 6 is a flow chart of a method for generating EUV light andperforming a lithography process using said EUV light, according to oneor more aspects of the present disclosure; and

FIG. 7 is a schematic view of a lithography system, in accordance withsome embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As the minimum feature size of semiconductor integrated circuits (ICs)has continued to shrink, there has continued to be a great interest inphotolithography systems and processes using radiation sources withshorter wavelengths. In view of this, extreme ultraviolet (EUV)radiation sources, processes, and systems (e.g., such as the lithographysystem 700 discussed with reference to FIG. 7) have been introduced.However, to make use of such system, light (or radiation) have awavelength in the EUV spectrum must be generated.

Referring to FIG. 1, illustrated therein is a schematic view of a EUVlight source. The EUV light source 100 of FIG. 1 is illustrative of anexemplary system that creates EUV wavelength radiation, which can bedelivered to a lithography system such as described in FIG. 7. In someembodiments, a EUV light source 100 may include a laser produced plasma(LPP) EUV light source. Thus, as shown and in some embodiments, the EUVlight source 100 may include a pulsed laser source 102 (e.g., such as aCO₂ laser) that generates a laser beam 104. The laser source 102 may bea gas discharge CO2 laser source (e.g., producing radiation at about10.6 μm). In other embodiments, other types of lasers may be suitable.The laser beam 104 may then be directed, by a beam transport and/orfocus system 106, to a EUV vessel 108. The chamber represented by thebox 106 of FIG. 1 may include various devices to perform variousfunctions including beam transport, beam focusing, beam amplification,and/or other suitable functionality. In some embodiments, the beamtransport and/or focus system 106 is collocated with (e.g., within achamber with or adjoining) the EUV vessel 108. In some embodiments, thelaser beam may travel (e.g., under vacuum environment) between the beamtransport and/or focus system 106 and the EUV vessel 108. In variousembodiments, the EUV vessel 108 also includes a droplet generator 110and a droplet catcher 112. In some cases, the droplet generator 110provides droplets (such as tin or a tin compound, discussed furtherbelow) into the EUV vessel 108.

In addition, the EUV vessel 108 may include one or more optical elementssuch as a collector 114. The collector 114 may also be referred to as acollector plate 114. In some embodiments, the collector 114 may includea normal incidence reflector, for example, implemented as a multilayermirror (MLM). For example, the collector 114 may include a siliconcarbide (SiC) substrate coated with a Mo/Si multilayer. In some cases,one or more barrier layers may be formed at each interface of the MLM,for example, to block thermally-induced interlayer diffusion. In someexamples, other substrate materials may be used for the collector 114such as Al, Si, or other type of substrate materials. The collector 114may be an ellipsoid-shape with an aperture (or opening) at the center toallow the laser beam 104 to pass through and reach the irradiationregion 116. Thus, in some embodiments, the laser beam passes through theaperture of the collector 114 and irradiates droplets generated by thedroplet generator 110, thereby producing a plasma at an irradiationregion 116. In some embodiments, the collector 114 may have a firstfocus at the irradiation region 116 and a second focus at anintermediate focus region 118. By way of example, the plasma generatedat the irradiation region 116 produces EUV light 124 collected by thecollector 114 and output from the EUV vessel 108 through theintermediate focus region 118. From there, the EUV light 124 may betransmitted to an EUV lithography system 120 for processing of asemiconductor substrate (e.g., such as discussed with reference to FIG.7).

The laser beam 104 may be generated by the source 102 and provided fromthe source 102 with a Gaussian distribution in a transverse plane. Insome systems, the laser beam 104 with the Gaussian distribution entersthe irradiation region 116 and may be incident a tin droplet. However,this impact by a Gaussian distribution beam may not be ideal, includingfor example with respect to the tin droplet shape. Thus, presented inthe present disclosure in some embodiments are methods and devices thatprovide for modifying the laser beam 104 providing for example, avariation in the distribution of intensity of the beam—also referred toa shape of the beam. Some of the beam shaping devices and methods mayincrease the collection efficiency, reduce undesired reflection, and/orsave collector wear.

In some embodiments, the laser beam from the source is modified byshaping the beam; the shaping may be performed between the laser source102 and the irradiation region 116. In some embodiments, the shaping ofthe beam is performed after the beam passes through portions of a beamtransport and/or focus system (e.g., such as beam transport and/or focussystem 106) and prior to the irradiation region 116. The EUV lightsource 100 includes an exemplary beam shaping unit 126. In someembodiments, the beam shaping unit 126 may be located anywhere in thesystem 100 such that the beam 104 from the source 102 enters the beamshaping unit 126 prior to the collector 114 or irradiation region 116.In some embodiments, the beam shaping unit 126 may be located in thesystem 100 such that the beam 104 from the source 102 enters the beamshaping unit 126 prior to the focal unit (e.g., mirror) that directs thebeam to the irradiation region 116.

In an embodiment, the beam shaping unit 126 is operable to modify ortransform the beam 104 from a Gaussian distribution in the transverseplane (as provided by the source 102), to a ring-shaped (orring-profiled) semi-Gaussian beam in the transverse plane. (This mayalso be referred to as a “donut” shape.) In some embodiments, thistransformation is accomplished by an inner and outer cone of areflaxicon, as discussed in further detail below. A reflaxicon, orreflective axicon, can be a specialized lens-type system that cantransform a beam into another shape, like a ring.

Referring to the example of FIG. 1, the effects of the beam shaping unit126 are illustrated. The laser beam 104 having a Gaussian destruction,which is illustrated as shape (or distribution) 104A, is provided to thebeam shaping unit 126. The shape 104A is circular in the cross-section(along a z-axis) as illustrated in FIG. 3A/3B. While the beam shapingunit 126 has an input of the shape 104A, the unit 126 outputs a modifiedbeam specifically, a shaped beam 128. The shaped beam 128 has aring-like, semi-Gaussian shape or distribution 128A (also referred to as“donut” shaped). Thereafter, the shaped laser beam 128 is provided tothe irradiation region 116. In some embodiments, the shaped laser beam128 has a ring-shaped semi-Gaussian beam in the transverse plan as adistribution, illustrated as 128A when it impacts the stream ofdroplets/mist in the irradiation region 116.

The beam transport and/or focus system 106 may in some embodimentsinclude a mask element 402 that provides for patterning the laser beamprior to being incident the stream of droplets/mists in the irradiationregion. The mask element 402 may block off portions of the beam,including, for example, deflecting portions of the shaped beam 128. Themask element may include a beam dump such as a water-cooled beam dump.In some embodiments, the laser beam is defected into a beam dump (e.g.,water cooled beam dump), while the non-deflected portion is provided asshaped beam 128A. In an embodiment, the mask element 402 includes adeflecting wedge (see 402A of FIG. 4). The wedge 402A may be included inconjunction with the beam dump. For example, the wedge 402A may deflecta beam portion into the beam dump (e.g., water-cooled beam dump). Themask element 402 and the beam shaping unit 126 may be implementedconcurrently in the EUV light source 100. In other embodiments, one ofthe mask element 402 or the beam shaping unit 126 may be omitted. Asdiscussed above, the laser beam 104 enters the beam shaping unit 126 andexits as shaped beam 128. As also discussed above, in an embodiment, thelaser beam 104 has a Gaussian distribution shape 104A and the shapedlaser beam 128 has a ring-shaped beam 128A. More specifically, theshaped laser beam 128 may be incident the mask element 402, which mayfurther modify the beam by patterning the ring-shaped beam such that oneor more portions of the ring-shaped beam are deflected as discussedfurther below. In other embodiments, the beam shaping unit 126 isomitted and the mask element 402 may modify the beam 104 having theGaussian distribution shape 104A to deflect one or more portions of thatbeam.

In some embodiments, at least one focusing element (e.g., mirror) isdisposed in the chamber of the beam transport and/or focus system 106between the beam shaping unit 126 and the collector 114. In someembodiments, at least one focusing element (e.g., mirror) is disposedbetween the mask element 402 and the collector 114. This element may bea portion of plurality of elements referred to as a final focusingassembly, which is discussed further below.

In some embodiments, the shaped beam 128 (with or without the patterningprovided by the mask element) then irradiates (e.g., impacts) a dropletin the irradiation region 116. This irradiation provides a reflectedportion 130 of EUV light, which is directed by the collector 114 to theintermediate focal point 118. Details of this interaction are describedin greater detail below with reference to FIGS. 2A, 2B, and 2C. The EUVlight 130 is generated by converting a material droplet (liquid or mist)into a plasma state when the material has an element, e.g., xenon,lithium or tin, indium, antimony, tellurium, aluminum, etc., with anemission line in the EUV spectrum.

The generated EUV light, illustrated as reflected portions 130, areelectromagnetic radiation having wavelengths of around 50 nm or less(also sometimes referred to as soft x-rays), and including light at awavelength centered around about 13.5 nm. The generated EUV light can beused in photolithography processes to produce features on targetsubstrates such as discussed below.

Referring to FIG. 2A, illustrated are diagrammatic views of portions ofan EUV vessel 108, which provide further details that may be applied tothe system of FIG. 1. FIG. 2A shows a diagrammatic view of including thecollector 114 and an entry of the shaped laser beam 128 through thecollector aperture and incident a droplet 204 in the irradiation region116. A final mirror of the preceding system (e.g., focusing unit 106) isillustrated as mirror 202. As discussed herein, in embodiments of thetraditional systems, the mirror 202 can be impacted by the EUVirradiation through the collector 114 central hole and also impacted bya thermal effect from absorption of the EUV irradiation and backward CO2radiation.

The droplet 204 may be spherical in shape or ellipsoidal in shape. Asdiscussed below, the droplet 204 may be a liquid droplet or in mistform. The droplet 204 may be tin or a tin compound. Example compositionsinclude, but are not limited to, tin, SnBr₄, SnBr₂, SnH₄, tin-galliumalloys, tin-indium alloys, tin-indium-gallium alloys or combinationsthereof. The distribution (or shape) 128A of the laser beam 128illustrates the peak amplitude of the beam with respect to a verticalaxis of 0. As discussed above, the beam 128 has a ring-shapedsemi-Gaussian beam in the transverse plane. In an embodiment, the shape128A is to scale with respect to the (tin) droplet 204 as illustrated inFIG. 2A. That is, the high amplitude points of the distribution 128A areincident an edge region of the droplet 204, while a low amplitudeportion is incident a center region of the droplet 204. The distribution128A provides a ring-shape in the cross-section such as illustrated withrespect to FIGS. 3A/3B. As such, the high amplitude regions may beincident the edge region around the circumference of the droplet 204.The distribution 128A may provide a larger incident surface area on thedroplet 204 than that of a Gaussian-shaped beam would have provided.This is furthered by allowing more contact with the curved surface ofthe droplet 204. Because of the larger surface area of the shaped beam128 (e.g., as compared to a Gaussian beam) onto the droplet 204, ahigher percentage of reflection of the EUV light to the collector 114for collection can be achieved. It is again noted that the shaped beam128 can be implemented for a pre-pulse (PP) or main pulse of the laser.As such, in some embodiments, the shaped beam 128 is incident a liquiddroplet; in some embodiments, the shaped beam 128 is incident a mistform “droplet”. During a method of EUV generation, the shaped beam 128may be incident droplets in both forms (e.g., PP followed by a MP).

FIG. 2B is a sequential diagrammatic view provided after the beam 128 isincident the droplet 204. It is noted that in some embodiments, apre-pulse is incident a droplet 204 (e.g., tin liquid droplet) and amain pulse is incident a “droplet” 204 in mist form (e.g., expanding adroplet to form a mist such as expanding tin mist). Again, for ease ofreference and understanding, the contacted material is referred to as a“droplet” 204, which may refer to either mist form or liquid dropletform. FIG. 2B illustrates a reflected EUV light 130 generated from theinteraction of beam 128 to the droplet/mist 204. That is, the laser beam128 goes through the hole of the collector 114 and impacts with thedroplets (mist) such as illustrated by droplet (mist) 204. The droplets(mists) 204 (e.g., tin) plasmas are generated and irradiate EUVemission, illustrated as EUV light 130. In some embodiments, as thelaser beam 128 provides a ring-shaped surface area of impact to thedroplet/mist 204 in one or both of the pre-pulse and main pulse, the EUVlight generated also is formed in a ring-shaped profile. Thus, theaperture or hole of the collector 114 may fall within the center of thering-shaped profile of EUV light. As illustrated in FIG. 2B, thereflected EUV light 130 is greater off-horizontal axis thanon-horizontal axis. That is the angular distribution of the reflectedEUV light 130 is increased. This can increase the efficiency as theon-horizontal axis light can be considered wasted in the system as it isnot captured and directed to the focal point 118 by the collector 114but traverses back through the aperture. It is noted that in anexemplary embodiment, the collector 114 may be approximately 24 inchesin diameter with a 4 inch diameter hole in the center. The reflected EUVlight 130 is angularly distributed such that it is incident the mirroredsurface of the collector 114 (as opposed reflecting to the opening inthe collector). The EUV light 130 is collected and focused to a focalpoint such as focal point 118 of FIG. 1. In addition to the EUV lightbeing undesirably “wasted” with respect to the lithography process if itpasses back through the opening in the collector 114, the reflectedlight passes back through the opening (referred to as “lost EUV light”)can also cause issues with the system 100. For example, the lost EUVlight can be absorbed by nearby mirrors in the beam transport and/orfocus system 106, which can create thermal dissipation and/orstabilization issues.

FIG. 2C illustrates that a portion of the laser 128 is also reflectedback from the droplet 204, illustrated as 128′. The reflected laser 128′may be CO₂ laser reflection. In some embodiments, it may be desirable toreduce the reflection of the CO₂ laser from the droplet/mist 204 toavoid damage to the laser system (CO2 laser system) and/or EUVirradiation system. In some embodiments, the reflected beam 128′ isreduced as compared to a reflected laser quantity if the droplet/mist204 were to be struck by the laser 104 having the distribution 104A asthe surface area of the interaction is increased as discussed above.FIG. 2C may occur contemporaneously with that of FIG. 2B.

It is noted that in FIGS. 2A, 2B, and 2C, the droplet/mist 204 iselliptical (also referred as a “pancake” shape) in the cross-sectionalview. In other embodiments, the droplet 204 may be approximatelyspherical. The elliptical shape may be provided by introducing apre-pulse of the laser (e.g., CO₂ laser) from source 102 prior to theintroduction of a main-pulse of the laser. The pre-pulse may be used toshape the droplet 204 increasing the available surface area for impactwith a subsequent main pulse (e.g., beam 128) of the laser. In someembodiments, the pre-pulse beam may have a Gaussian shape such as 104A.In a further embodiment, the main-pulse following the Gaussian pre-pulsemay be provided as beam 128 having a ring-like in shape as illustratedin FIG. 2A. In some embodiments, the pre-pulse beam may also have aring-like shape such as 128A. As such, in a further embodiment, each ofthe main-pulse and the pre-pulse may have a ring-like shape such asdistribution 128A.

It is noted that FIGS. 2A, 2B, 2C provide a simplification in one ormore aspects of providing a beam to a target droplet/mist. FIG. 2D isillustrative of the differing states and dispositions of the droplet 204at pre-pulse and main pulse stages of the process. For example, thepre-pulse (PP) may be incident a droplet 204 in liquid droplet form,while the main pulse (MP) may be incident the droplet 204 after itsexpansion and when it is in mist form. In some embodiments, the droplet204 has a trajectory between the PP and MP, for example, is disposed ata different location within the system.

With respect to one or more embodiments discussed herein and asdiscussed above, a pre-pulse (PP) maybe incident on a droplet 204, inits liquid form. Providing the shaped beam incident the liquid formdroplet may provide for the droplet 204 to expand to the mist (e.g. from30 micrometer to 300 micrometer in diameter). The main pulse of thelaser (MP) (shaped) may then be incident the droplet 204 in mist form.If pre-pulse beam shape is ring-like or “donut” shaped when incident thedroplet, the beam (e.g., CO2 laser) reflection back to system can belowered as illustrated above. If a main pulse (MP) shape is a “donut”shape when incident the droplet 204, then in expanding mist form, notonly can the beam reflection (e.g., CO2 laser) back to system becomelower as discussed above, but in some embodiments the angular radiationpattern of generated EUV radiation can changed. This modification ofshape can provide for one or more of (1) less EUV radiation waste due tocollector central aperture, (2) less EUV radiation reflected back toirradiate on the last few mirrors (e.g., mirror 202), thereby providingan extended mirror lifetime with less thermal effect for operation, (3)more uniform angular distribution on collector surface, or (4) moresurface area of droplet (e.g., mist) can be hit by a main pulse for moreEUV irradiation as well as laser-to-EUV conversion efficiency.

Referring now to FIGS. 3A/3B, illustrated is an embodiment of the beamtransport and focusing system 106 including the beam shaping unit 126.The beam transport and/or focus system 106 of FIGS. 3A/3B may be used inthe EUV light source 100 of FIG. 1. The beam transport and/or focussystem 106 includes a plurality of mirrors 302 which deflect and/orfocus the laser beams. The mirrors 302 are exemplary only and notintended to be limiting in number, configuration, or arrangement.

FIG. 3A illustrates a first embodiment of processing the main pulse andpre-pulse of the laser 104 using the beam transport and/or focus system106. FIG. 3B illustrates a second embodiment of processing the mainpulse and the pre-pulse of the laser 104 using the beam transport and/orfocus system 106.

FIG. 3B illustrates in an embodiment, the mirrors 302 direct the mainpulse of the laser beam 104 through the beam shaping unit 126, while themirrors 302 direct the pre-pulse of the laser beam 104 such that it isnot influenced by the beam shaping unit 126. Thus, the pre-pulse beam104 may maintain its shape with a Gaussian distribution shape 104A whenexiting the system 106 to the irradiation region 116. However, otherembodiments are possible including where both the pre-pulse and the mainpulse of the laser beam 104 are directed to and through the beam shapingunit 126 as illustrated in the embodiment of FIG. 3A. Here, as in FIG.3A, the beam 128 may include a main pulse and/or a pre-pulse beam eachhaving a distribution similar to 128A.

Regarding FIG. 3A/3B from a system implementation perspective, in anembodiment, the beam shaping unit 126 includes a reflaxicon asillustrated in FIGS. 3A/3B. The reflaxicon includes an outer-cone 304and an inner-cone 306. The inner-cone 306 and the outer-cone 304 aredisposed coaxially. A central opening 308 is created that defines aninner and outer diameter of the ring shape 128A. In some embodiments, awindow 310 is disposed on the reflaxicon. The window 310 may includeZnSe, diamond, or other suitable material. The inner cone 306 may bemounted on the window 310. While a reflaxicon is one exemplaryembodiment of a device that may be used to implement the shaping of thebeam 104 to provide the shaped beam 128 implementation of other devicesmay also be possible including other reflective optics.

Referring now to FIG. 4, illustrated is an embodiment of the beamtransport and/or focus system 106 which may be used in the system 100 ofFIG. 1 and/or include one or more elements of the beam transport and/orfocus system 106 described above with reference to FIGS. 3A/3B. FIG. 4illustrates for some embodiments a mask element 402 is included in thebeam transport and/or focus system 106. In an embodiment, the maskelement 402 is disposed after the beam shaping unit 126 and prior to afinal focusing element 106B (referred to as Final Focal Assembly or FFA)of the beam transport and/or focus system 106. The mask element 402 isdisposed such that it defines patterns to be applied to the beam 128prior to the beam 128 being incident the droplet 204. The mask element402 may include a mirror or other suitable material operable to deflectportions of a laser beam including wedges, beam dumps and other suitablematerials. The patterned laser beam, subsequent passing through the maskelement, is illustrated as patterned beam 404 having a distribution 404Ain FIG. 4. The distribution 404A is exemplary only and in otherembodiments other portions of the beam may be deflected or a pluralityof portions of the beam may be deflected. In an embodiment, the maskelement 402 includes a deflecting wedge 402A. The deflecting wedge 402Amay act as a masking element deflecting portions of the beam. In anembodiment, the deflecting wedge 402A is operable to rotate to aposition desired to deflect said portion of the beam. As discussedabove, the mask element 402 may also include a beam dump. For example,in the illustration of FIG. 4, the wedge 402A may be positioned todeflect radiation from an upper right quadrant of the beam. In otherembodiments, the wedge 402A may be rotated to other positions, e.g.,rotated to “6 o'clock” using a clock as analogous to the beam shape todeflect a respective portion of the beam. In some embodiments, the maskelement 402 may include air-cooled or water-cooled beam dumps. The beamdumps may be selected for the suitable wavelength of the incident beam.The wedge 402A may provide deflected beam portions to a correspondingbeam dump.

In an embodiment, the pattern provided by the mask element 402 isdetermined by a process whereby a defect is identified on a collector,such as the collector 114, that is to be used in generating the EUVlight source. The defect may be determined by inspection of thecollector, analysis of data of EUV light generation performance,analysis of data as to implementation of the EUV light source in alithography patterning process, and/or other suitable methods. In anembodiment, data collected on the performance of imaging a criticaldimension (CD) feature or uniformity of CD features to be formed on atarget substrate (e.g., wafer) is used to determine the presence of adefect on the collector. In some embodiments, an element (e.g., mirror)disposed in the system after the immediate focus point (e.g., 118) maybe used to determine the presence of a defect on the collector. In anembodiment, the identification of the defect includes determining acoordinate of the defect on the collector. Using the example of FIG. 4,a defect 406 is identified. In an embodiment, the defect 406 is tindebris. In an embodiment, the defect 406 is damage to a surface of thecollector 114.

After identifying the presence of the defect(s) such as defect 406, thepattern of the mask element 402 (including in some embodiments, wedge402A) is designed, selected, and/or provided such that the EUV radiationgenerated from the laser beam impacting the droplet/mist 204 isdecreased or eliminated in collector region having the defect whileincreased in non-defect regions. As illustrated in the embodiment ofFIG. 4, the EUV light 130 is greater in a non-defect region than theregion surrounding the defect 406 due to the patterning of the beam 128to form the beam 404.

Referring now to FIG. 5, illustrated is an embodiment of a collector114. The collector 114 of FIG. 5 may be implemented in the system 100 ofFIG. 1, and or provided as the collector of the embodiments discussedabove such as that of FIG. 2A, 2B, 2C, 3A, 3B, or 4. Illustrated in FIG.5, a laser beam 404 is provided through the hole in the collector 114 tothe irradiation region 116 where it is incident a droplet 204. The laserbeam 404 may be shaped to be a ring-type beam, such as discussed abovewith reference to the laser beam 128. The laser beam 404 may also bepatterned (e.g., via a mask element), such as discussed above withreference to the beam 404 of FIG. 4. As illustrated due to themodification of the shape of the beam 404, there is a greater generationof EUV light from the droplet 204 to be provided to a first region ofthe collector 114 (e.g., top of collector 114 relative to FIG. 5orientation) than provided to a second region of the collector (e.g.,bottom of the collector 114 relative to FIG. 5 orientation).

In some embodiments, the collector 114 is rotatable, as illustrated byexemplary rotation 502. In an embodiment, the collector 114 isazimuthally-rotatable. The rotation of the collector 114 may be used inconjunction with the patterning of the beam 404 by a mask element inorder to achieve a greater percentage of EUV incident a defect-freeportion of the collector 114 than a defect-containing portion of thecollector 114. For example, the collector 114 is rotated such that thedefect 406 is located away from a region of increased EUV light 130generation.

Referring now to FIG. 6, illustrated is flow chart of a method 600 formodifying a laser beam to be used in an EUV light source, according toone or more aspects of the present disclosure. It is noted that theprocess steps of the method 600, including any descriptions given withreference to the figures, are merely exemplary and are not intended tobe limiting beyond what is specifically recited in the claims thatfollow. Moreover, additional process steps may be implemented before,during, and after the method 600, and some process steps may be replacedor eliminated in accordance with various embodiments of the method 600.

The method 600 begins at block 602 where an EUV light source system isconfigured with suitable beam modification elements, according to one ormore aspects of the present disclosure. The beam modification elementsmay be disposed in the light source system. By way of example, and insome embodiments, the EUV light source system may be the EUV lightsource system 100, as shown in FIG. 1. As such, in various embodiments,the EUV light source system may include beam modification elements suchas the beam shaping unit discussed with reference to FIGS. 1, 2A, 2B,2C, 3A, 3B, and 4; the masking element for patterning the beam discussedwith reference to FIGS. 1, 4, and 5; the rotatable collector of FIGS. 1and 6; and/or other suitable beam modification elements that provide forconfiguring the providing, reflection, or collection of a light (bymanipulation of the laser beam, the EUV light, or the collector of theEUV light).

In an embodiment, the light source is configured such that a beamshaping unit is disposed in the path of the laser beam provided from alaser source. The beam shaping unit is disposed prior to the laser beamentering the irradiation region (e.g., prior to passing through thecollector). The EUV light source may also be configured with otherdevices for shaping the laser beam such as, a mask element forpatterning the laser beam. The mask element may be substantially similarto as discussed above with reference to FIG. 4. The EUV light sourcesystem may also be configured to allow for rotation of the collectorbefore or during processing such as described above with reference toFIG. 5.

The method 600 then proceeds to block 604 where a defect is determinedon the collector of the EUV light system. The defect may be determinedby inspection of the collector, analysis of data of EUV light generationperformance, analysis of data as to implementation of the EUV lightsource in a lithography patterning process, and/or other suitablemethods. In an embodiment, data collected on the performance of imaginga critical dimension (CD) feature or uniformity of CD features on atarget substrate (e.g., wafer) is used to determine the presence of adefect on the collector. In an embodiment, the identification of thedefect includes determining a coordinate of the defect on the collector.In some embodiments, the method 600 may also be used to maintaincollector operation lifetime as discussed herein.

In an embodiment of the method 600, block 604 is omitted and/or analysisis performed that provides that the collector does not include a defectrequiring corrective action.

The method 600 then proceeds to block 606 where a mask element isprovided and/or the collector is azimuthally-rotated to modify the beamintensity based on the presence of a defect determined in block 604. Themask element provided may be substantially similar to the mask element402 discussed above with reference to FIG. 4. The collector may berotated substantially similar to as discussed above with reference toFIG. 5. The block 606 may provide for increasing the beam intensity at aregion of the collector spaced a distance from the defect, whiledecreasing the beam intensity at a region of the collector at the defectlocation.

In an embodiment of the method 600, block 606 is omitted.

The method 600 then proceeds to block 608 where EUV light is generatedusing the EUV light source provided in block 602. The EUV light may begenerated by providing a laser beam that has been shape modified toprovide a ring-like shape to a irradiation unit. In some embodiments,the laser beam is alternatively or additionally modified such that it ispatterned. The laser beam may be patterned using the mask element suchas discussed above. One or more of the shape modification and patterningmay be performed prior to the laser beam being incident the droplet. Insome embodiments, the collector is rotated before or during theprovision of the laser beam as discussed above with reference to block606 and/or with reference to FIG. 5. The provided laser beam (e.g.,shape modified and/or patterned) generates reflected EUV light from thedroplet. The reflected EUV light is collected by the collector andprovided to a focal point. Subsequently, the reflected EUV light isprovided to a EUV lithography system where it is used to pattern atarget wafer as discussed below.

Referring now to block 610 of the method 600, as previously noted, theEUV light source described above may be used to provide an EUV lightsource for a lithography system. By way of illustration, and withreference to FIG. 7, provided therein is a schematic view of anexemplary lithography system 700, in accordance with some embodiments.The lithography system 700 may also be generically referred to as ascanner that is operable to perform lithographic processes includingexposure with a respective radiation source and in a particular exposuremode. In at least some of the present embodiments, the lithographysystem 700 includes an extreme ultraviolet (EUV) lithography systemdesigned to expose a resist layer by EUV light (e.g., provided via theEUV vessel). Inasmuch, in various embodiments, the resist layer includesa material sensitive to the EUV light (e.g., an EUV resist). Thelithography system 700 of FIG. 7 includes a plurality of subsystems suchas a radiation source 702 (e.g., such as the EUV light source 100 ofFIG. 1), an illuminator 704, a mask stage 706 configured to receive amask 708, projection optics 710, and a substrate stage 718 configured toreceive a semiconductor substrate (e.g., wafer) 716. A generaldescription of the operation of the lithography system 700 may be givenas follows: EUV light from the radiation source 702 is directed towardthe illuminator 704 (which includes a set of reflective mirrors) andprojected onto the reflective mask 708. A reflected mask image isdirected toward the projection optics 710, which focuses the EUV lightand projects the EUV light onto the semiconductor substrate 716 toexpose an EUV resist layer deposited thereupon. Additionally, in variousexamples, each subsystem of the lithography system 700 may be housed in,and thus operate within, a high-vacuum environment, for example, toreduce atmospheric absorption of EUV light.

In the embodiments described herein, the radiation source 702 may besubstantially similar to the EUV light source 100 and/or may be more ormore devices configured to receive EUV light from the EUV light source100. As discussed above, the source may generate the EUV light using alaser produced plasma (LPP). In some examples, the EUV light producedand provided the system 700 may include light having a wavelengthranging from about 1 nm to about 100 nm. In one particular example, theradiation source 702 generates EUV light with a wavelength centered atabout 13.5 nm.

Upon receipt, the EUV radiation (e.g., received/generated by theradiation source 702) is directed toward the illuminator 704. In someembodiments, the illuminator 704 may include reflective optics (e.g.,for the EUV lithography system 700), such as a single mirror or a mirrorsystem having multiple mirrors in order to direct light from theradiation source 702 onto the mask stage 706, and particularly to themask 708 secured on the mask stage 706. In some examples, theilluminator 704 may include a zone plate, for example, to improve focusof the EUV light. In some embodiments, the illuminator 704 may beconfigured to shape the EUV light passing therethrough in accordancewith a particular pupil shape, and including for example, a dipoleshape, a quadrapole shape, an annular shape, a single beam shape, amultiple beam shape, and/or a combination thereof. In some embodiments,the illuminator 704 is operable to configure the mirrors (i.e., of theilluminator 704) to provide a desired illumination to the mask 708. Inone example, the mirrors of the illuminator 704 are configurable toreflect EUV light to different illumination positions. In someembodiments, a stage prior to the illuminator 704 may additionallyinclude other configurable mirrors that may be used to direct the EUVlight to different illumination positions within the mirrors of theilluminator 704. In some embodiments, the illuminator 704 is configuredto provide an on-axis illumination (ONI) to the mask 708. In someembodiments, the illuminator 704 is configured to provide an off-axisillumination (OAI) to the mask 708. It should be noted that the opticsemployed in the EUV lithography system 700, and in particular opticsused for the illuminator 704 and the projection optics 710, may includemirrors having multilayer thin-film coatings known as Bragg reflectors.By way of example, such a multilayer thin-film coating may includealternating layers of Mo and Si, which provides for high reflectivity atEUV wavelengths (e.g., about 13 nm).

As discussed above, the lithography system 700 also includes the maskstage 706 configured to secure the mask 708. Since the lithographysystem 700 may be housed in, and thus operate within, a high-vacuumenvironment, the mask stage 706 may include an electrostatic chuck(e-chuck) to secure the mask 708. As with the optics of the EUVlithography system 700, the mask 708 is also reflective. As illustratedin the example of FIG. 7, light is reflected from the mask 708 anddirected towards the projection optics 710, which collects the EUV lightreflected from the mask 708. By way of example, the EUV light collectedby the projection optics 710 (reflected from the mask 708) carries animage of the pattern defined by the mask 708. In various embodiments,the projection optics 710 provides for imaging the pattern of the mask708 onto the semiconductor substrate 716 secured on the substrate stage718 of the lithography system 700. In particular, in variousembodiments, the projection optics 710 focuses the collected EUV lightand projects the EUV light onto the semiconductor substrate 716 toexpose an EUV resist layer deposited on the semiconductor substrate 716.As described above, the projection optics 710 may include reflectiveoptics, as used in EUV lithography systems such as the lithographysystem 700. In some embodiments, the illuminator 704 and the projectionoptics 710 are collectively referred to as an optical module of thelithography system 700.

In some embodiments, the lithography system 700 also includes a pupilphase modulator 712 to modulate an optical phase of the EUV lightdirected from the mask 708, such that the light has a phase distributionalong a projection pupil plane 714.

As discussed above, the lithography system 700 also includes thesubstrate stage 718 to secure the semiconductor substrate 716 to bepatterned. In various embodiments, the semiconductor substrate 716includes a semiconductor wafer, such as a silicon wafer, germaniumwafer, silicon-germanium wafer, III-V wafer, or other type of wafer asdescribed above or as known in the art. The semiconductor substrate 716may be coated with a resist layer (e.g., an EUV resist layer) sensitiveto EUV light. To be sure, the lithography system 700 may further includeother modules or subsystems which may be integrated with (or be coupledto) one or more of the subsystems or components described herein.

To be clear, the lithography system 700 is presented such that it isunderstood that the EUV light source system 100 may be used as thesource 702 or provide the EUV radiation to the source 702 for use by thelithography system 700. That is, the system 100 provides the EUVradiation to an intermediate focal point 118, at which point it istransferred to the systems described in the lithography system 700.

The various embodiments described herein offer several advantages overthe existing art. It will be understood that not all advantages havebeen necessarily discussed herein, no particular advantage is requiredfor all embodiments, and other embodiments may offer differentadvantages. For example, by creating a ring-like pattern of the laserbeam that is incident the target droplet, a greater surface area can beaccessed. In some embodiments, providing a ring-like laser beam incidentthe target droplet generates a ring-like pattern of EUV emission thatcan be projected onto the collector surface. In some embodiments, thiscan decrease the lost in the system of EUV light by reducing the amountof EUV light that is lost through the aperture in the collector. In someembodiments, decreasing the amount of EUV lost can improve theefficiency of the system, reduce heat generation, provide for higherthermal stability, and/or other advantageous features. In someembodiments, by using a mask pattern and/or a rotatable collector, thefar-field pattern can be optimized for better slit uniformity. In someembodiments presented, there may also be an increased life time of thecollector device. This can be on account of the ability to continue touse the collector in creation of the EUV light despite the presence of adefect or debris as the EUV light can be directed away from the point ofdefect/debris. Example methods of directing the EUV light away from thedefect/debris portion include use of a mask element and/or rotatablecollector. It is noted that continuing to process with the debris/defectwithout accounting for the EUV light incident that debris/defect regioncan impact the performance of a lithography system such as the system700 described above because the EUV light can be absorbed or notreflected by the debris/defect region.

Thus, one of the embodiments of the present disclosure a method includesproviding a laser beam from a laser source. A shape of the laser beam isthen modified. The modified beam is incident a tin droplet to generatean EUV light. This EUV light is reflected using a collector. In anembodiment, the modifying the shape of the laser beam includes providinga ring-profile laser beam. In an embodiment, the providing the laserbeam includes providing a Gaussian shaped beam. In an embodiment, themodifying of the shape is performed by a reflaxicon device. In anembodiment, the modifying the shape of the laser beam includespatterning the laser beam to block a first portion of the beam andmaintain a second portion of the beam. In an embodiment, the patterningof the laser beam is performed by providing a mask element in a path ofthe laser beam. In an embodiment, the modifying the shape of the laserbeam includes altering the laser beam from a Gaussian shape to aring-like shape. In an embodiment, the modifying the shape furtherincludes passing the ring-like shape beam through a mask element toblock a portion of the ring-like shape beam. In an embodiment, thecollector is rotated based on a location of the blocked portion of thering-like shape beam. In an embodiment, a pattern for the mask elementis selected using an analysis of a critical dimension (CD) feature on atarget substrate.

In another of the embodiments, discussed is a method including providinga laser beam having a Gaussian distribution. The laser beam is modifiedfrom a Gaussian distribution to a ring-like distribution. The modifiedlaser beam is provided through an aperture in a collector. The modifiedlaser beam interfaces with a tin droplet, which generates an extremeultraviolet (EUV) wavelength light. The generated EUV wavelength lightis provided to the collector away from the aperture. In an embodiment,the laser beam is provided by a CO₂ laser source. In some embodiments,the tin droplet is in mist form; in some embodiments, the tin droplet isin liquid form; in some embodiments, the tin droplet is during themethod at times in liquid form (e.g., PP) and at times in mist form(e.g., MP). In an embodiment, modifying the laser beam is performed by areflaxicon. In an embodiment, a portion of the modified laser beam isblocked prior to interfacing the modified laser beam with the tindroplet. In an embodiment, the method includes rotating the collector.In an embodiment, modifying the laser beam includes modifying a mainpulse of the laser beam while a pre-pulse of the laser beam ismaintained as a Gaussian distribution when interfacing the tin droplet.

In yet another of the embodiments, discussed is an extreme ultraviolet(EUV) source system including a laser source operable to provide a laserbeam, an irradiation region operable to receive a plurality of dropletsfor generating an EUV light, a collector operable to collect and reflectthe EUV light from the plurality of droplets; and a reflaxiconinterposing the laser source and the collector. In an embodiment, a maskelement is disposed between the reflaxicon and the collector. In anembodiment, at least one mirror operable to focus the laser beamdisposed between the mask element and the collector. In an embodiment,the collector is operable to be azimuthally-rotatable.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: providing a laser beam froma laser source; modifying a shape of the laser beam to form a modifiedlaser beam, wherein the modifying the shape of the laser beam includesaltering the laser beam from a Gaussian shape to a ring-like shape;contacting a tin droplet with the modified laser beam to generate an EUVlight; and reflecting the EUV light using a collector.
 2. The method ofclaim 1, wherein the modifying the shape of the laser beam includesproviding the ring-like shape by a reflaxicon device.
 3. The method ofclaim 2, wherein the Gaussian shaped beam is incident a first end of thereflaxicon device.
 4. The method of claim 2, wherein the ring-like shapeis output a second end of the reflaxicon device.
 5. The method of claim1, wherein the modifying the shape of the laser beam includes patterningthe laser beam to deflect a first portion of the laser beam and maintaina second portion of the laser beam, wherein the deflected first portionis deflected into a beam dump.
 6. The method of claim 5, wherein thedeflected first portion is deflected into the beam dump including awater cooled beam dump by a wedge.
 7. The method of claim 1, wherein themodifying the shape further comprises: passing the laser beam having thering-like shape through a mask element to deflect a portion of the laserbeam having the ring-like shape.
 8. The method of claim 7, furthercomprising: rotating the collector based on a location of the deflectedportion of the laser beam.
 9. The method of claim 7, further comprising:selecting a pattern for the mask element using an analysis of a criticaldimension (CD) feature on a target substrate.
 10. A method, comprising:providing a laser beam having a Gaussian distribution; modifying thelaser beam from the Gaussian distribution to a ring-like distribution;providing the modified laser beam through an aperture in a collectorplate; interfacing the modified laser beam with a tin droplet, whereinthe interfacing generates an extreme ultraviolet (EUV) wavelength light;and wherein the generated EUV wavelength light is provided to thecollector plate away from the aperture.
 11. The method of claim 10,wherein the tin droplet is in mist form.
 12. The method of claim 10,wherein the modifying the laser beam is performed by a reflaxicon. 13.The method of claim 10, further comprising: deflecting a portion of themodified laser beam prior to interfacing the modified laser beam withthe tin droplet.
 14. The method of claim 10, further comprising:rotating the collector plate.
 15. The method of claim 10, wherein themodifying the laser beam includes modifying a main pulse of the laserbeam and wherein a pre-pulse of the laser beam is maintained as aGaussian distribution when interfacing the tin droplet.
 16. An extremeultraviolet (EUV) source system, comprising: a laser source operable toprovide a laser beam; an irradiation region operable to receive aplurality of droplets for generating an EUV light; a collector operableto collect and reflect the EUV light from the plurality of droplets; anda reflaxicon interposing the laser source and the collector, wherein thereflaxicon includes a first portion and a second portion and an openingdefined between the first and second portions, wherein the openingdefines an inner diameter and outer diameter of a ring-shape.
 17. TheEUV source system of claim 16, further comprising: a mask elementbetween the reflaxicon and the collector.
 18. The EUV source system ofclaim 17, at least one mirror operable to focus the laser beam disposedbetween the mask element and the collector.
 19. The EUV source system ofclaim 16, wherein the collector is operable to be azimuthally-rotatable.20. The EUV source system of claim 16, wherein the first portion is aninner cone and the second portion is an outer cone, the inner and outercones disposed coaxially.